From 14a7225dea86df0f288f94df174e3d1fcd0a18ed Mon Sep 17 00:00:00 2001 From: Srinivas Pandruvada Date: Thu, 6 Nov 2025 17:34:09 -0800 Subject: [PATCH] cpufreq: intel_pstate: Check IDA feature only during MSR 0x199 write Commit 0fb5be7fea98 ("cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode") introduced a check for feature X86_FEATURE_IDA to verify turbo mode support. Although this is the correct way to check for turbo mode, it causes issues on some platforms that disable turbo during OS boot but enable it later. Without this feature check, users were able to write 0 to /sys/devices/system/cpu/intel_pstate/no_turbo post-boot to get turbo mode frequencies. To restore the old behavior while still addressing the unchecked MSR issue on some Skylake-X systems, limit the X86_FEATURE_IDA check to only when setting MSR 0x199 Turbo Engage Bit (bit 32). Fixes: 0fb5be7fea98 ("cpufreq: intel_pstate: Unchecked MSR aceess in legacy mode") Signed-off-by: Srinivas Pandruvada --- drivers/cpufreq/intel_pstate.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index 43e847e9f741..38a8e877f222 100644 --- a/drivers/cpufreq/intel_pstate.c +++ b/drivers/cpufreq/intel_pstate.c @@ -598,9 +598,6 @@ static bool turbo_is_disabled(void) { u64 misc_en; - if (!cpu_feature_enabled(X86_FEATURE_IDA)) - return true; - rdmsrl(MSR_IA32_MISC_ENABLE, misc_en); return !!(misc_en & MSR_IA32_MISC_ENABLE_TURBO_DISABLE); @@ -2014,7 +2011,8 @@ static u64 atom_get_val(struct cpudata *cpudata, int pstate) u32 vid; val = (u64)pstate << 8; - if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled)) + if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) && + cpu_feature_enabled(X86_FEATURE_IDA)) val |= (u64)1 << 32; vid_fp = cpudata->vid.min + mul_fp( @@ -2179,7 +2177,8 @@ static u64 core_get_val(struct cpudata *cpudata, int pstate) u64 val; val = (u64)pstate << 8; - if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled)) + if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled) && + cpu_feature_enabled(X86_FEATURE_IDA)) val |= (u64)1 << 32; return val; -- 2.43.0